U.S. Pat. No. 3,642,728, herein incorporated by reference, teaches a new class of sulfonated polymers which are derived from polymers containing olefinic unsaturation, especially elastomeric polymers, e.g. butyl and ethylenepropylene terpolymers. These materials may be neutralized with organic amines or basic materials selected from Groups I, II, III, IV, V, VI-B, VII-B and VIII and mixtures thereof of the Periodic Table of Elements. These materials, especially the butyl and the ethylene-propylene terpolymer (EPDM) derivatives, may broadly be classified as thermoelastomers, that is these materials may be processed at high temperatures by use of shear force in the presence of selected polar additives and yet at the temperature of use, e.g. room temperature, the materials, through the association of the sulfonate group behave as cross-linked elastomers. Thus, these materials represent one form of reprocessable elastomers, which are very desirable in industry.
However, although these materials are commercially useful, the melt viscosity even at very high temperature tends to be sufficiently high as to preclude the use of conventional plastic fabrication techniques. Thus, the very purpose for which these compounds are derived is not adequately fulfilled. In this invention, it has unexpectedly been discovered that decreased melt viscosity may be obtained by combining these polymers with a minor portion of a polystyrene thermoplastic resin or a sulfonated polystyrene in a heterogeneous polymer blend. Further, it has been unexpectedly discovered that the tensile properties of these blends, as measured at room temperature, can be substantially improved as compared to the sulfonated elastomers alone.
The sulfonated elastomers described in U.S. Pat. No. 3,647,728, herein incorporated by reference, when used as gums possess a relatively low level of rigidity or stiffness which yields rather limp materials incapable of supporting themselves when prepared in thin sections. This is a major limitation, if one desires to prepare dimensionally stable parts, e.g. automotive or appliance applications. It is known in the art that stiffness of elastomers may be increased by the combination of carbon black or inorganic material such as clays, calcium carbonate or silicates, etc. However, these materials, while increasing the hardness, further deteriorate the melt viscosity of the above-described ionic elastomers. Thus, systems which at best have borderline processability even at very low metal sulfonate levels further deteriorate in their flow behavior and thus cannot be processed at all. It has unexpectedly been discovered that in the compositions of the instant invention, wherein minor amounts of the unsulfonated or sulfonated polystyrene are combined with the sulfonated elastomers described above, result in increased tensile modulus at room temperature.
Thus, this invention teaches compositions of matter which represent significant improvement over the prior art in that low melt viscosity is obtained at no loss in tensile properties.
The present application is related to two other filed applications Ser. Nos. 514,502, now U.S. Pat. No. 3,905,586 and 514,512, now U.S. Pat. No. 3,923,370, herein incorporated by reference. These two applications, which have issued, are related to elastomeric blends of a crystalline polyolefinic resin and a neutralized sulfonated elastomeric blends. These blends are of a homogeneous nature, wherein the crystalline polyolefinic resin appears completely soluble in the sulfonated elastomeric polymer at elevated temperatures. The melt rheology and tensile properties of these homogeneous blends are improved as compared to the unmodified sulfonated elastomeric polymer due to the plasticization of the polymeric backbone of the elastomeric polymer. However, the blending of an inorganic filler with neutralized sulfonated elastomeric polymer creates a heterogeneous blend, wherein the rheological and physical properties are adversely affected due to incomplete interfacial bonding between the inorganic particles and the elastomeric matrix. Blends of a neutralized sulfonated elastomeric polymer and a polystyrene thermoplastic resin or a sulfonated polystyrene thermoplastic resin, wherein the thermoplastic resin is at a concentration level in excess of 20 parts per hundred by weight based on 100 parts of the neutralized sulfonated elastomeric polymer, exhibit a general deterioration in physical properties due to the manifestation of gross incompatibility. Surprisingly, it has been found that the incorporation of the polystyrene or sulfonated polystyrene at a concentration level of below about 20 parts per hundred by weight results in compositions exhibiting both improved physical and rheological properties.